EP0084037B1 - Control device for the supply pressure of a supercharged combustion engine - Google Patents

Description

State of the art

The invention is based on a device for influencing the boost pressure of an internal combustion engine operated with supercharging depending on the operating parameters.

Such a device is already known from the unpublished EP-A-46872, in which the contracting states FR, GB, SE are named. However, EP-A-46872 focuses on special problems that occur when charging an Otto engine equipped with a throttle valve, in particular a regulation of the pressure difference before and after the throttle valve is proposed.

From JP-A-55-29 033 a boost pressure control dependent on the speed and the metered amount of fuel is known by means of a function generator. A bypass valve is acted upon by the signals from the function generator and controls the pressure prevailing there on the outlet side of a turbocharger.

US-A-4174 617 discloses throttle valve or load-dependent control of the boost pressure in an Otto engine. This citation is based on the task of compensating for pressure fluctuations in the outside air, in particular as a function of the height above sea level.

An electronic control system of an exhaust gas turbocharger for the internal combustion engine of a motor vehicle is known from the unpublished EP-A-0 040 814, in which the contracting states DE, GB are named. The exhaust gas flow required to operate the turbine is controlled by means of a bypass which can be influenced in its effect. The basic control signals required to control the open position of the bypass are taken from a memory located in the control circuit depending on the operating variables of the internal combustion engine. The intake air mass, the mixture composition, the engine temperature, the ignition angle and the engine speed are taken into account as operating parameters. When knocking occurs, these basic control signals are modified so that the knocking disappears.

With the known devices, however, the advantages of a turbocharger, particularly in the case of serious load changes, cannot be used satisfactorily.

The invention has for its object to make the advantages of charging usable even in the non-stationary operation of an internal combustion engine. This problem is solved by the device with the characterizing features of the main claim.

Advantages of the invention

The device according to the invention has the advantage over the known that, in addition to the operating parameters of exhaust gas or air temperature and barometric height, the acceleration of the internal combustion engine is also used to influence the boost pressure. In addition, the direct measurement of the boost pressure enables boost pressure regulation to a setpoint value corresponding to the operating state of the internal combustion engine.

drawing

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. 1 shows a characteristic diagram for the boost pressure as a function of load and speed in a supercharged engine, FIG. 2 shows an exemplary embodiment in the block diagram of the devices for controlling the boost pressure according to the invention, FIG. 3 and FIG. 4 show two possibilities of bypass signal boxes and finally FIGS. 5 and 6 show two Alternatives to air-side boost pressure control.

Description of the embodiments

The exemplary embodiments relate to boost pressure controls in an internal combustion engine with auto-ignition. In this machine, the boost pressure is controlled and, if necessary, regulated according to a predetermined map, load and engine speed being used as map variables, boost pressure or air flow rate or air volume per stroke serving as the output variable. Figure 1 shows such a map. A lowering of the boost pressure with increasing engine speed can be seen, which can be seen as a clear departure from the principle of maximum value limitation. Using this map, pressure values determined from tests for each operating point of the internal combustion engine can be determined, these points representing compromises between the most varied of aspects, such as power, exhaust gas composition, soot discharge, etc.

FIG. 2 shows a block diagram of a charge pressure regulator, in which the setpoint is determined using a map. The supercharger device is designated by 10, and a turbine 11 with a bypass duct 12, the inlet opening of which is controllable by means of a valve 13, is shown in a rough schematic view. A controller and an interlocking (mechanical, pneumatic, electrical,) are marked with the reference number 15, a servo force which in the end actuating the valve 13 being fed in via a input 16 in the case of a special interlocking type. The electrical controller input has the reference number 17. It is preceded by a setpoint / actual value comparison stage 18. The setpoint is formed on the basis of load and speed signals from corresponding sensors 19 and 20 in a characteristic diagram 21, which is followed by a correction stage 22. This correction stage 22 has a control input 23 for correction quantities such as signals relating to the atmospheric height, the exhaust gas temperature, the air temperature or the acceleration. A pressure signal from a pressure sensor 25, to which a corresponding waveform stage 26 is connected, arrives at the actual value comparison stage 18 as the actual value. Instead of the pressure sensor, an air quantity can also be used Sor or an air mass sensor can be attached, since there is usually a certain relationship between the boost pressure and the amount of air supplied per stroke.

In principle, all sizes are possible as a load signal from the load sensor 19, which enable a statement to be made about the amount of fuel just injected into the diesel engine. Mention should be made, for example, of the injection duration of the injection valves, the control rod position and the adjustment lever position of an injection pump, the torque delivered, etc.

The boost pressure associated with a specific operating state is determined from the characteristic diagram 21, the absolute value of the boost pressure preferably being stored. Depending on the application, storage as overpressure or underpressure is of course also possible.

The map 21 itself is preferably electronic in nature. For example, digital value memories (PROM) are used. The further processing of the map value is also carried out electronically, but for some applications, purely mechanical devices are certainly also z. B. useful with a space cam.

• - je nach barometrischer Höhe einen anderen Ladedruck einzuregeln,
• - den Ladedruck so zu regeln, dass die Abgastemperatur einen vorgegebenen Wert nicht überschreitet,
• - bei Beschleunigung kurzzeitig einen höheren Ladedruck anzusteuern bzw. die den Turbolader beeinflussende Einrichtungen, wie Bypass oder ähnliches kurzzeitig so zu steuern, dass die höchstmögliche Beschleunigung erreicht wird.

Since it is not possible to take into account all influencing variables in an internal combustion engine by means of a three-dimensional map 21, the map 22 is followed by the correction stage 22. The map values are then manipulated in this block, for example to

• - regulate a different boost pressure depending on the barometric height,
• - regulate the boost pressure so that the exhaust gas temperature does not exceed a predetermined value,
• - briefly control a higher boost pressure during acceleration or briefly control the devices influencing the turbocharger, such as bypass or the like, in such a way that the highest possible acceleration is achieved.

The boost pressure setpoint value corrected in this way is then fed to the setpoint / actual value comparison stage 18, at which the control difference from the actually existing boost pressure is formed.

The subsequent controller 15 then, together with the manipulated value, influences the exhaust gas passage cross section through the bypass opening in such a way and until the setpoint and actual value match.

Depending on the type of internal combustion engine and the application, it is advisable to specify the controller's P, D or I behavior, although combinations are of course also possible.

FIG. 3 shows a possible implementation of a signal box for influencing the bypass valve 13, a pressure medium serving as servo pressure, which acts on a membrane signal box 31 via a controllable pressure regulator. A membrane 32 of the signal box 31 is loaded by a spring 33 and the bypass valve 13 can then be opened more or less via the settings of the pressure regulator 30. The print medium is e.g. Compressed air from the compressed air braking system of the vehicle (truck). Pressure regulators 30 themselves are accessible as such and are known in various possible variations.

FIG. 4 shows a further possibility for controlling the bypass valve 13 by means of a solenoid valve 35, which is actuated in cycles, in a pressure line 36, which leads to the pressure chamber of the membrane interlocking 31. In this case, the solenoid valve 35 receives pulse-length-modulated control signals which depend on the setpoint / actual value deviation and whose generation is not a problem for a person skilled in the art in the field in question.

With the described control of the boost pressure or the air throughput according to predetermined characteristic maps by influencing the effective exhaust gas flow cross-section on the turbine, it results that when the boost pressure is reduced compared to the unaffected turbine, the turbocharger speed is reduced. If the accelerator is suddenly accelerated, the turbocharger must first be accelerated and boost pressure built up to avoid a smoke burst.

It is advantageous to always keep the turbocharger at as high a speed as possible in order to get boost pressure as quickly as possible (acceleration) and thus increased air filling of the cylinder.

This can be achieved by not influencing the exhaust gas cross section as described above, but by blowing off air from the intake manifold.

This is shown in Figures 5 and 6.

The signal box 40 is controlled in accordance with the boost pressure (or air flow rate) map in such a way that excess air is blown off and the desired boost pressure is established. 5, the blown air is added back to the exhaust gas stream in front of the turbine.

As less work has to be done on the compressor side due to the limited pressure, the charging speed increases. As protection against damage to the turbocharger, it may be necessary to limit the speed of the turbocharger by in turn directing part of the gas flow in the bypass 41 past the turbine. The charger speed n ₂ is therefore preferably processed in a controller 42 for controlling the bypass 41. Too high a supercharger speed opens the bypass and thus limits the supercharger speed to a safe level (P or PI controller). As an alternative to the supercharger speed, the exhaust gas back pressure Pa can also be used to control the bypass 41 in such a way that excessive exhaust gas back pressure opens the bypass 41 (or another mechanism that determines the flow cross-section of the turbine, such as "variable flow turbine") so the back pressure is limited.

Of course, the individual signal boxes 40, 41 can be influenced by correction variables; especially when accelerating the individual signal boxes can be closed or severely throttled.

FIG. 6 shows a likewise possible arrangement in which the blown-off air is introduced after the turbine, but otherwise the same control mechanisms apply.

The arrangement according to FIG. 6 has the advantage that the exhaust gas temperature at the turbine inlet fluctuates less than that according to FIG. 5 and a larger control range (up to intake manifold pressure = atmospheric pressure) is also possible. Depending on the design, however, a lower turbocharger speed must be accepted.

An advantage of the air blow-off control (regulation) compared to the exhaust gas bypass solution from FIGS. 2 to 4 is that the turbocharger is kept at high speed and thus high boost pressure is quickly available when the load changes / accelerates.

It is essential in all of the exemplary embodiments described above that a load and speed-dependent free specification of the boost pressure with any increasing, falling or constant characteristic enables a reduction in the pollutant emissions, in particular at a higher engine speed (approximately from half the nominal engine speed). The specification of the boost pressure to be set in each case or the corresponding amount of air takes place in a map. This provides optimal conditions for economical and low-emission operation for every operating point of the machine. At the same time, the load on the internal combustion engine is reduced due to the lowering of the peak combustion pressure at high engine speeds.

Claims (7)

1. Device for influencing the charging pressure of an internal combustion engine operated with supercharge, dependent on operating characteristics, by the use of a characteristic diagram memory arrangement, in which operating set values for determining the charging pressure are stored, with only one characteristic diagram memory (21), in which the operating set values are entered load- and speed-dependently, these operating set values being correctable dependent on the operating characteristics by correction variables, characterized in that at least one of the variables used as operating characteristics is acceleration of the internal combustion engine, exhaust or air temperature and barometric level, and in that the charging pressure actual value measured directly with a sensor can be regulated to adjustable charging pressure set values.

2. Device according to Claim 1, characterized in that the influencing of the charging pressure takes place by means of a spring-loaded diaphragm controlling unit (31) in a bypass channel (12).

3. Device according to Claim 2, characterized in that the diaphragm controlling unit (31) is actuated by means of a pressure medium via a pressure controller (30) or an electromagnetically operable valve (35).

4. Device according to at least one of the preceding claims, characterized in that the effective cross-section of the valve (13) is controlled by means of electric motor and linkage, stepping motor, linear solenoid actuator or hydraulic positioner.

5. Device according to at least one of the preceding claims, characterized in that a controllable connection is provided from the charging pressure side of the internal combustion engine to the exhaust pipe upstream or downstream of the turbine (11).

6. Device according to at least Claims 1 to 5, characterized in that a bypass channel (12) controlled dependent on operating characteristics bridges the turbine (11).

7. Device according to Claim 1, characterized in that at least one of the variables used as a further operating characteristic is supercharger speed and exhaust pressure.

Images